Yeah I seem to be in the minority in that I find it hard to get upset here. In fact, the lesson I take away is that if you, as a company--especially a highly visible one, do any sort of A/B testing which might be remotely seen as manipulating behavior by anyone (which covers broad ground), you probably shouldn't make it public.
I'm not sure I see how this is all that different from running a bunch of ads with different messages and/or emotional content and seeing how they differential ly perform.
Yup, that's the big issue in my opinion. Their TOS never had research as condition that you accept. When Reddit decided to use their data-set for research and make it available, they had a public blog post explicitly calling it out and had an option to disable your data for research. Naturally I opted out. I was informed of the change and I acted on it. Those users on Facebook never agreed to the research component of the ToS (because it didn't exist yet), did not know they were involved, and were included in a PNAS study that had Cornell researchers involved.
I'm not sure I see how this is all that different from running a bunch of ads with different messages and/or emotional content and seeing how they differential ly perform.